EKO / ENGINEERING TOOLS

Bending calculators.

Estimate bending force, calculate flat length, or find K-factor from a test bend.

01 / Your bending parameters

Thickness T · mm Bend length L · mm V-die opening · mm Material Material factor Capacity allowance · %Optional extra allowance for preliminary selection. Part name / note (optional)

02 / ESTIMATED BENDING FORCE

— tf

— kN

Force per metre—tf / m

With capacity allowance—tf · reference only

Die opening / thickness—

Bend length—m

tf means metric tonne-force. 1 tf = 9.80665 kN. This is bending force, not hydraulic pressure in MPa.

Preliminary estimate only. Confirm material properties and machine and tooling load limits before production.

03 / Compare your parts

Part	Material	T / L / V (mm)	Factor	tf / m	Total tf	Total kN	Allowance %	With allowance tf	Action

Enter your parameters and select “Add to comparison” to save a result here.

Comparison records stay in this page only. Export your CSV before refreshing or closing it.

Formula, assumptions & limitations

This calculator uses the simplified formula in the supplied bending reference chart, “calculation form.pdf”, printed pages 72–73.

Force (tf) = 68 × T² ÷ V × (L ÷ 1000) × material factor
With allowance = force × (1 + allowance % ÷ 100)

T is thickness in mm, V is the die opening in mm, and L is bend length in mm. The base material is carbon steel with a stated strength range of 45–50 kgf/mm². Approximate chart factors are 0.50 for soft copper and soft aluminium, 1.00 for hard aluminium, and 1.50 for stainless steel. Actual grades and tempers vary.

The simplified formula does not interpolate the chart. For example, T = 3 mm and V = 24 mm gives 25.50 tf/m; the source table lists 27.0 tf/m. A separate tensile-strength correction method from the source is not combined with this formula.

The source assumes an 88° die opening angle; smaller angles require more force. These estimates do not cover bottoming or coining. Check material properties, tooling limits and machine capacity, especially concentrated loads. An added allowance does not certify that a machine or tool is suitable.

Enter your actual die opening. This calculator does not automatically select tooling.

Need help selecting a press brake for your parts?

Discuss your requirements ↗

01 / Input dimensions All lengths in mm

Thickness TMeasured inside radius RAngle conventionAngle (°)Dimension conventionOutside dimension AOutside dimension BMeasured flat length before bending L

Use the measured angle and inside radius after springback. Follow the selected dimension convention; do not mix inside, outside and tangent dimensions.

02 / Calculated K-factor

—

K = neutral-axis distance from inside / thickness

Bend allowance BA—

Bend deduction BD—

Outside setback OSSB—

Bend angle θ—

How to measure your part

Measure outside dimensions A and B to the virtual intersection of the extended outside faces. Tangent lengths a and b exclude the bend arc. This 90° diagram is illustrative and is not drawn to scale for your inputs.

Formulas, scope & references

β = θ × π / 180；θ = 180° − α
BA = β × (R + K × T)
OSSB = (R + T) × tan(θ / 2)
BD = 2 × OSSB − BA
Outside dimensions: L = A + B − BD
Tangent lengths: L = a + b + BA
Reverse calculation: K = (BA / β − R) / T

For one circular bend in uniform-thickness sheet, with a bend angle strictly between 0° and 180°. Not suitable for closed hems or complex forming. K depends on material, thickness, actual radius, tooling and process; thickness and radius alone do not determine it. Validate with repeated test bends under the same conditions. Four decimal places do not imply measurement accuracy.

K-factor definition and BA formula: SOLIDWORKS · K-Factor. Other formulas follow from single-bend circular geometry. K is the neutral-axis distance from the inside face divided by thickness. Check the definition used by other software before transferring values.